In general, a circuit board comprises a plurality of conductive circuits made of such as copper. For electronic signal transmission or power signal transmission, a plurality of electrically connecting pads is extended from the conductive circuits. Furthermore, a Ni/Au layer can be formed on the exposed surface of the electrically connecting pads such that conductive components such as gold wires and solder balls can effectively be coupled to the electrically connecting pads through the Ni/Au layer. In addition, the Ni/Au layer can effectively isolate the electrically connecting pads from ambient air and thus protect the electrically connecting pads from being oxidized by the ambient air. The electrically connecting pads can be such as bonding fingers with a Ni/Au layer formed thereon. During a wire bonding process, since the gold wires and the Ni/Au layer of the bonding fingers comprises same material, the gold wires and the bonding fingers can be electrically coupled together. The electrically connecting pads also can be bump pads or ball pads with a Ni/Au layer formed thereon. The Ni/Au layer can protect the bump pads or the ball pads made of such as copper from being oxidized by ambient air, thereby improving electrical connection quality between the bump or ball pads and bumps or balls mounted to the bump pads or ball pads.
FIGS. 1A to 1C show a conventional metal electroplating process. As shown in FIG. 1A, a circuit board 1 having a patterned circuit layer 11 defined thereon is provided and a solder mask layer 12 is formed on the circuit board 1. The solder mask layer 12 has a plurality of openings 12a such that electrically connecting pads 110 and electroplating lines 111 of the circuit layer 11 can be exposed from the openings 12a. Therein, the electroplating lines 111 are used as a current conductive path in a subsequent electroplating process. As shown in FIG. 1B, a patterned resist layer 13 having a plurality of openings 131 is formed on the circuit board 1 such that the electroplating lines 111 can be covered by the patterned resist layer 13 while the electrically connecting pads 110 can be exposed from the openings 131. By using the electroplating lines 111 as a current conductive path, an electroplating process is performed. As a result, a Ni/Au layer 14 is formed on the electrically connecting pads 110 exposed from the solder mask layer 13. After the resist layer 13 is removed, an etching process is performed so as to remove the electroplating lines 111 that are not covered by the Ni/Au layer, thereby cutting off the electrical connection between the electroplating lines 111 and the electrically connecting pads 110.
According to the above process, since the resist layer 13 needs to be deposited on the preformed solder mask layer 12 and the electroplating lines 111 having different height at the same time, it becomes impossible to make the patterned resist layer 13 closely attached to the electroplating lines 111. Instead, the lower portion of the resist layer 13 formed on the electroplating lines 111 becomes narrower than the upper portion of the resist layer 13. Accordingly, during the subsequent electroplating process, the Ni/Au material is easy to permeate into the electroplating lines 111 underneath the resist layer 13, thereby forming a permeation portion 14a on the electroplating lines 111, as shown in FIG. 1c. Because the electroplating lines 111 with the permeation portion 14a thereon is difficult to be removed by etching, electrical connection between the electrically connecting pads and the electroplating lines can not be efficiently cut off. As a result, electrical performance of the circuit board and the product yield are adversely affected.
Accordingly, there is a need to develop a metal electroplating process which can efficiently prevent permeation of Ni/Au material to the electroplating lines in the prior art.